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how do you launch a roller coaster without a launch hill?

the clue
We're Katie and Devyn, and we tried to figure out how to launch a coasting car using springs. We modified my brother's Pinewood Derby car from Cub Scouts and put a spring in it. We compressed the spring and launched the car up a racetrack hill. With one spring, the car went a little ways up the hill, but not far. So we tried two springs and got better results, but it was hard to compress both springs. It would be hard to launch a coaster filled with people this way. Do you have any better ideas?
whiz quiz
What's the record for fastest land speed in a car?

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